1. Field of the Invention
The present invention relates to an electrical part mounting apparatus and method suitable for electrical connection between two electrical parts.
2. Description of the Related Art
Before explaining a conventional electrical part mounting apparatus and method, the structure in which electrical parts are connected will be described with reference to FIGS. 11A and 11B.
As shown in FIGS. 11A and 11B, a plurality of conductive wires 2 and 3, each formed of an ITO film (a transparent resistive film made of indium tin oxide) or the like, are formed on an insulating plate 1 of glass or the like, thereby constituting an electrical part 4.
A plurality of conductive members (bumps) 6 and 7 are formed on the lower surface of a frame 5, thereby constituting another electrical part 8 such as an IC chip.
The conductive members 6 and 7 of the electrical part 8 are placed opposed to the conductive wires 2 and 3 on the insulating plate 1, and the electrical parts 4 and 8 are bonded to each other by a thermosetting anisotropic conductive material 10 made of a thermosetting epoxy adhesive containing conductive particles 9, or the like. The conductive members 6 and the conductive wires 2, and the conductive members 7 and the conductive wires 3, which are aligned vertically, are connected via the conductive particles 9.
A conventional electrical part mounting apparatus and method for obtaining such a connecting structure will be described with reference to FIGS. 17 to 20.
The conventional electrical part mounting apparatus is, as shown in FIGS. 17 to 20, provided with a flat support 50, and a pressure head 51 having a flat lower surface and supported movably in the vertical direction with respect to the support 50. The pressure head 51 is lowered by a hydraulic cylinder (not shown) at a fixed speed while being heated.
The electrical part mounting method employed in such a mounting apparatus will be described with reference to FIGS. 17 to 20.
As shown in FIG. 17, the electrical part 4, the thermosetting anisotropic conductive material 10 shaped like a film (hereinafter abbreviated as ACF), and the electrical part 8 are laid in order on the flat support 50.
In the first step, the pressure head 51, which has been heated to about 220xc2x0 C., is moved downward by the hydraulic cylinder at a fixed moving speed (about 30 mm/sec) that is somewhat slow, and brought into contact with the electrical part 8, as shown in FIG. 18.
The fixed moving speed is set to be somewhat slow so that the electrical parts 4 and 8 are not damaged.
In the second step, a fixed pressure is applied to the pressure head 51 to press the electrical part 8.
The electrical part 8 is heated by the heated pressure head 51, and then, the ACF 10 is heated to a liquid state by the heated electrical part 8.
As a result, the pressure head 51 moves down and the conductive particles 9 sandwiched between the conductive wires 2 and 3 and the conductive members 6 and 7 are crushed, so that the conductive wires 2 and 3 are electrically connected to the conductive members 6 and 7, respectively, as shown in FIG. 11B.
In the third step, the heated pressure head 51 is cooled.
Then, the ACF 10 is set, the electrical parts 4 and 8 are bonded to each other, and the conductive wires 2 and 3 are connected to the conductive members 6 and 7, respectively.
In the fourth step, the pressure head 51 is moved up, and mounting of the electrical parts is completed.
As mentioned above, in the conventional electrical part mounting apparatus and method, since the heated pressure head 51 moves a fixed moving speed that is somewhat slow, working efficiency is low, which results in low productivity.
Furthermore, since the pressure head 51 is brought into contact with the electrical part 8 at the fixed slow moving speed, parallelism between the flat lower surface of the pressure head 51 and the flat surface of the support 50 is impaired. Moreover, since the pressure head 51 presses the electrical part 8 with a fixed pressure in this state, it presses the electrical part 8, the ACF 10, and the electrical part 4 without sufficient parallelism.
When the ACF 10 is liquefied in this state, the conductive particles 9 are crushed at one end of the electrical parts, and are not crushed at the other end. This causes unstable electrical connection between the conductive wires 2 and 3 and the conductive members 6 and 7, respectively.
Furthermore, since the ACF 10 is abruptly liquefied by the heated pressure head 51 in the conventional electrical part mounting method, the adhesive therein expands and bubbles are produced between the electrical parts 4 and 8, which decreases the adhesive force between the electrical parts 4 and 8.
Still furthermore, air is left between the electrical parts 4 and 8 due to abrupt liquefaction, and turned into bubbles, which also weakens the adhesion between the electrical parts 4 and 8.
In addition, since the pressure head 51 descends rapidly due to abrupt liquefaction, it cannot move straight in the vertical direction. Therefore, the conductive particles 9 are crushed at one end of the electrical parts and not crushed at the other end, which results in unstable electrical connection between the conductive wires 2 and 3 and the conductive members 6 and 7, respectively.
Accordingly, it is an object of the present invention to provide an electrical part mounting apparatus and method suitable for electrical connection between two electrical parts that can freely adjust the pressure and moving speed of a pressure head.
According to a first aspect of the present invention, there is provided an electrical part mounting apparatus including a pressure head for pressing an electrical part, a heater for heating the pressure head, a pressure measuring member for measuring the pressure of the pressure head against the electrical part, and a moving speed control member for controlling the moving speed of the pressure head.
The electrical part mounting apparatus may further include a timer for measuring the pressing time and/or the heating time of the pressure head for the electrical part, and a temperature control member for controlling the temperature of the heater.
According to a second aspect of the present invention, there is provided an electrical part mounting method wherein a heated pressure head for pressing an electrical part laid on a thermosetting anisotropic conductive material presses the electrical part while gradually increasing the pressure to a required pressure.
According to a third aspect of the present invention, there is provided an electrical part mounting method wherein a heated pressure head for pressing an electrical part laid on a thermosetting anisotropic conductive material presses the electrical part while increasing the pressure stepwise to a required pressure.
According to a fourth aspect of the present invention, there is provided an electrical part mounting method wherein a heated pressure head for pressing an electrical part laid on a thermosetting anisotropic conductive material presses the electrical part with a first pressure applied thereto, and then presses the electrical part with a second pressure higher than the first pressure.
Preferably, the first pressure is about ⅓ of the second pressure.
According to a fifth aspect of the present invention, there is provided an electrical part mounting method wherein a pressure head is lowered at high speed near an electrical part laid on a thermosetting anisotropic conductive material, and then, lowered gently until it is brought into light contact with the electrical part.
According to a sixth aspect of the present invention, there is provided an electrical part mounting method wherein two electrical parts are electrically connected by semi-setting a thermosetting anisotropic conductive material and then, heating and pressing the semi-set thermosetting anisotropic conductive material.
According to a seventh aspect of the present invention, there is provided an electrical part mounting method including the steps of forming a semi-set thermosetting anisotropic conductive material on an insulating plate with a conductive wire, and heating and pressing an electrical part, such as an IC chip, on the semi-set thermosetting anisotropic conductive material.
Preferably, the thermosetting anisotropic conductive material is laid in the form of a sheet on the insulating plate and semi-set by being heated and pressed by a pressure head, and the electrical part is heated and pressed by the pressure head.
Preferably, the temperature at which the electrical part is heated is higher than the heating temperature to semi-set the thermosetting anisotropic conductive material.
Preferably, the thermosetting anisotropic conductive material is semi-set at 80xc2x0 C. to 120xc2x0 C. and the electrical part is heated at 180xc2x0 C. to 250xc2x0 C.